The overall aim is to further our understanding of the mechanisms bacteria employ to regulate gene expression and enzyme activity in a complex biosynthetic pathway. In the past eight years, we have gained an overall view of the regulation of aromatic acid synthesis in B. subtilis. This project will extend many of these physiological studies to the molecular level. We will focus primarily on those observations which represent novel and unique aspects of regulation which may provide fresh insight into regulation of other systems in other organisms. This will include the purification and characterization of the enzymes which transaminate tyrosine, phenylalanine and histidinol phosphate. The regulation control of these transaminases will also be investigated. We will also attempt to understand the molecular basis of cross-pathway regulation between the pathways of histidine and aromatic acid synthesis. The understanding of how the end product of one pathway regulates gene expression and enzyme activity in an unrelated pathway requires that we understand how gene expression is regulated by its cognate end products. Therefore we will investigate the production and regulation control of messenger RNA translated from the tryptophane operon of B. subtilis.